JP2004073956A - Paint film forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a paint film excellent in appearance, curability, and water resistance industrially stably. <P>SOLUTION: In the method, the paint film is formed on a substrate by two coat one bake from a high-solid type clear paint 400-550 in VOC (volatile org. compound) in the diluted paint diluted to be coating viscosity which is a water-base paint containing a carboxyl group-containing resin and a tertiary amine -60 to 0 mV in half-equivalent point electric potential by potentiometric titration and 120-290°C in boiling point in an amount of 1.5-7.0 equivalent of the carboxyl group of the resin and a carboxylic acid-epoxy group curing paint. <P>COPYRIGHT: (C)2004,JPO

Description

（式中、Ｒは水素原子又はメチル基、Ｘは化２式又は化３式で示す有機鎖である。）
【００７７】
【化２】

（式中、Ｙは炭素数２〜８の直鎖又は分岐鎖のアルキレン基、ｍは３〜７の整数、ｑは０〜４の整数である。）
【００７８】
【化３】

（式中、Ｒは水素原子又はメチル基、ｎは２〜５０の整数である。）
【００７９】
化１式に示す水酸基含有エチレン性不飽和モノマーの具体例としては、（メタ）アクリル酸２−ヒドロキシエチル、（メタ）アクリル酸２−ヒドロキシプロピル、（メタ）アクリル酸２−ヒドロキシブチル、（メタ）アクリル酸４−ヒドロキシブチル、（メタ）アクリル酸６−ヒドロキシヘキシル、およびこれらのε−カプロラクトンとの反応物、（メタ）アクリル酸と大過剰のジオール（例えば、１，４ブタンジオール、１，６ヘキサンジオール、ポリエチレングリコール、ポリプロピレングリコール）をエステル化した化合物などが例示される。
【００８０】
ここで用いる水酸基含有エチレン性不飽和モノマーとしては、炭素数が５〜２３、特に５〜１３のものを好ましく用いることができる。このモノマーの鎖長が短すぎると架橋点近傍のフレキシビリティがなくなるため固くなりすぎ、長すぎると架橋点間分子量が大きくなりすぎるからである。
【００８１】
上記水酸基含有エチレン性不飽和モノマーを用いると、得られる塗膜の密着性及びリコート性が向上する。また水酸基とカルボキシル基とを有するアクリル系ポリエポキシドは、後述するように、カルボキシル基とカルボン酸エステル基とを有する（ａ）アクリル系ポリカルボン酸と、水酸基及びエポキシ基の両方の官能基において反応し結合するので、より強固な塗膜を得ることができる。
【００８２】
アクリル系ポリエポキシドの水酸基価は５〜３００ｍｇＫＯＨ／ｇ（固形分）、好ましくは１０〜２００ｍｇＫＯＨ／ｇ（固形分）、より好ましくは１５〜１５０ｍｇＫＯＨ／ｇ（固形分）である。水酸基価が３００ｍｇＫＯＨ／ｇ（固形分）を超えると、塗料不揮発分が低下したり塗膜の耐水性が不足し、５ｍｇＫＯＨ／ｇ（固形分）未満では密着性に劣る。
【００８３】
本発明に用いて好適な（ｃ）ポリエポキシドは、前述の化１〜３式で示した構造の水酸基含有エチレン性不飽和モノマー５〜７０重量％と、（ｃ）−（１）エポキシ基含有エチレン性不飽和モノマー１０〜６０重量％と、必要に応じて水酸基及びエポキシ基の両方とも有しないエチレン性不飽和モノマー０〜８５重量％とを共重合することによって得られる。この場合、得られる（ｃ）ポリエポキシドは、１分子中にエポキシ基を平均で２〜１２個、より好ましくは３〜１０個、水酸基を平均で０．５〜１０個、より好ましくは１〜８個有する。
【００８４】
（ｃ）ポリエポキシド成分は、硬化性樹脂組成物中の全固形分の重量を基準として、１０〜８０重量％好ましくは２０〜７０重量％、より好ましくは３０〜６５重量％の量で配合することができる。ポリエポキシドの量が１０重量％より少ないと硬化性が低下し、８０重量％を超えると耐黄変性が悪化する。
【００８５】
本発明にいうハイソリッド型クリヤー塗料は、（ａ）アクリル系ポリカルボン酸と、（ｂ）ポリエステルポリカルボン酸と、（ｃ）ポリエポキシドとの３成分を混合することにより製造することができる。特にカルボキシル基とカルボン酸エステル基とを有する（ａ）アクリル系ポリカルボン酸を用い、水酸基とエポキシ基とを有する（ｃ）ポリエポキシドを用いた場合には、耐酸性に特に優れた塗膜を形成するハイソリッド型クリヤー塗料が得られる。
【００８６】
この場合、（ａ）アクリル系ポリカルボン酸及び（ｂ）ポリエステルポリカルボン酸に含有されるカルボキシル基と、（ｃ）ポリエポキシドに含有されるエポキシ基とのモル比が１／１．４〜１／０．６、好ましくは１／１．２〜１／０．８となり、かつ（ａ）アクリル系ポリカルボン酸に含有されるカルボキシル基又はカルボキシル基結合炭素に隣接する炭素に結合するカルボン酸エステル基と（ｂ）ポリエステルポリカルボン酸及び（ｃ）ポリエポキシドに含有される水酸基とのモル比が１／２．０〜１／０．５、より好ましくは１／１．５〜１／０．７となるような量で配合することが好ましい。
【００８７】
（ａ）アクリル系ポリカルボン酸及び（ｂ）ポリエステルポリカルボン酸に含有されるカルボキシル基と、（ｃ）ポリエポキシドに含有されるエポキシ基とのモル比が１／０．６を超えると得られる塗料の硬化性が低下し、１／１．４より小さくなると塗膜が黄変する。また、（ａ）アクリル系ポリカルボン酸に含有されるカルボキシル基又はカルボキシル基結合炭素に隣接する炭素に結合するカルボン酸エステル基と（ｂ）ポリエステルポリカルボン酸及び（ｃ）ポリエポキシドに含有される水酸基とのモル比が１／０．５を超えると得られる塗料の硬化性が低下し、１／２．０より小さくなると水酸基が過剰となるため耐水性が低下する。
【００８８】
このようにして得られるハイソリッド型クリヤー塗料の硬化機構は、先ず加熱により（ａ）アクリル系ポリカルボン酸中のカルボキシル基とカルボン酸エステル基とが反応して（ａ）アクリル系ポリカルボン酸中に酸無水物基が生成し、遊離のモノアルコールが生成する。生成したモノアルコールは蒸発して系外へ除去される。そして（ａ）アクリル系ポリカルボン酸中に生成した酸無水物基は（ｂ）ポリエステルポリカルボン酸及び（ｃ）ポリエポキシドに含有される水酸基と反応することにより架橋点を形成し、再度カルボキシル基を形成する。このカルボキシル基及び（ｂ）ポリエステルポリカルボン酸中に存在するカルボキシル基は、（ｃ）ポリエポキシド中に存在するエポキシ基と反応することにより架橋点を形成する。このように３種類のポリマーが相互に反応することにより硬化が進行し、高い密度で架橋した塗膜が形成される。
【００８９】
本発明にいうハイソリッド型クリヤー塗料中には、例えば４級アンモニウム塩などのような酸とエポキシとのエステル化反応に通常用いられる硬化触媒を含んでもよい。この硬化触媒としては、ベンジルトリエチルアンモニウムクロリド又はブロミド、テトラブチルアンモニウムクロリド又はブロミド、サリチレート又はグリコレート、パラトルエンスルホネートなどが例示される。
【００９０】
この硬化触媒の添加量は、樹脂組成物の固形分に対して一般に０．０１〜３．０重量％、好ましくは０．１〜１．５重量％、より好ましくは０．４〜１．２重量％である。硬化触媒の量が０．０１重量％より少ないと添加した効果が得られず、３．０重量％を超えて添加すると貯蔵安定性が低下する。
【００９１】
また本発明にいうハイソリッド型クリヤー塗料中には、特開平２−１５１６５１号公報などに開示されたスズ系の化合物を混合することもできる。このようなスズ系触媒としては、例えばジメチルスズビス（メチルマレート）、ジメチルスズビス（エチルマレート）、ジメチルスズビス（ブチルマレート）、ジブチルスズビス（ブチルマレート）などが挙げられる。
【００９２】
このスズ系触媒の添加量は、樹脂組成物の固形分に対して一般に０．０５〜６．０重量％、好ましくは０．１〜４．０重量％、より好ましくは０．２〜２．０重量％である。スズ系触媒の量が０．０５重量％より少ないと貯蔵安定性が低下し、６．０重量％を超えて添加すると耐候性が低下する。なお硬化触媒とスズ系触媒とを併用する場合には、硬化触媒とスズ系触媒の重量比は１／４〜１／０．２とすることが好ましい。
【００９３】
本発明にいうハイソリッド型クリヤー塗料には、架橋密度を上げ、耐水性の向上を計るために、ブロック化イソシアネートを加えることもできる。また公知の紫外線吸収剤、光安定剤、酸化防止剤などを添加してもよい。さらに公知のレオロジーコントロール剤、表面調整剤などを添加してもよいし、粘度調整などの目的でアルコール系溶剤、芳香族炭化水素系溶剤、エステル系溶剤、ケトン系溶剤などの溶剤を用いることもできる。
【００９４】
塗膜形成方法
本発明の塗膜形成方法では、水性ベース塗料と、希釈塗料におけるＶＯＣが４００〜５５０であるカルボン酸・エポキシ基硬化系のハイソリッド型クリヤー塗料とを２コート１ベーク塗装法により塗装する。上記ＶＯＣが、４００未満では形成される塗膜の表面平滑性が低下し、５５０を超えると所望の膜厚の確保が困難となる。尚、ＶＯＣとは、Ｖｏｌａｔｉｔｅ　Ｏｒｇａｎｉｃ　Ｃｏｍｐｏｕｎｄの略であり、希釈塗料の不揮発分と希釈塗料比重を実測し、下記式に代入することよって算出される値をいう。一般に、ＶＯＣが高いと、塗料中の不揮発分が少なくなり、ＶＯＣが低いと不揮発分が多くなると言うことである。
ＶＯＣ＝１０００×希釈塗料比重×（１−希釈塗料不揮発分／１００）
【００９５】
上記溶剤型クリヤー塗料を塗装粘度に希釈した状態とは、後述する静電塗装機の霧化方式、あるいは温度、湿度等の塗装環境等の要因を踏まえた経験的に求められた塗装粘度に、希釈用有機溶剤を用いて希釈され、粘度調整された状態を示すものである。一般に、温度が１５℃〜４０℃、湿度が１０〜９８％の範囲での塗装粘度は、２０〜５０秒（／２０℃・Ｎｏ．４フォードカップ）であることが好ましい。この範囲外ではタレ、ワキ等の外観上の不具合が発生し易い。更に好ましくは２２〜４０秒（／２０℃・Ｎｏ．４フォードカップ）である。
【００９６】
上記水性ベース塗料を自動車車体に塗装する場合には、一般にエアースプレー塗装、あるいは通称「ベル」と言われる回転霧化式の静電塗装機等により塗装され、所定時間のインターバルの後にクリヤー塗料が塗装される。
【００９７】
上記水性ベース塗料は、一般に乾燥膜厚が１０〜３０μｍとなる範囲で塗装される。この膜厚が３０μｍより厚い場合や、１０μｍより薄いと外観品質が低下する。また水性ベース塗料の塗布後のセッティング時間は、従来と同様に室温で３〜１５分とされる。このセッティング時間が３分より短いと焼付時にワキが生じる場合があり、１５分以上としても効果が飽和し埃などが付着するため好ましくない。更に、４０〜１００℃で３〜１５分程度プレヒートを施すこともできる。
【００９８】
また上記ハイソリッド型クリヤー塗料は、一般に乾燥膜厚が２５〜７０μｍとなる範囲で塗装される。この膜厚が７０μｍより厚くなるとタレが発生し、２５μｍより薄いと最終塗膜の膜厚に不足して外観品質が低下する。
【００９９】
上記ハイソリッドクリヤー塗料を塗布後のセッティング時間は、３〜１５分程度とされる。セッティング時間が３分より短いとワキが発生しやすく、１５分より長くなっても効果が飽和し埃などが付着するため好ましくない。
【０１００】
その後、両ウェット塗膜は１００〜１８０℃、好ましくは１２０〜１６０℃に加熱され、一体的に焼付硬化されて塗膜が形成される。焼付時間は温度によって異なるが、１２０〜１６０℃で１０〜３０分が適当である。
【０１０１】
【実施例】
以下、具体的な実施例を挙げて本発明を詳細に説明するが、本発明は以下の実施例により限定されるものではない。尚、以下に於いて「部」とあるのは「重量部」を意味する。
【０１０２】
製造例
塗膜形成性樹脂の製造１
窒素導入管、撹拌機、温度調節機、滴下ロートおよび冷却管を備えた２Ｌの反応容器にプロピレングリコールエチルエーテル４５０部を仕込んで、温度を１０７℃とした。次に、アクリルアミド１００部をプロピレングリコールメチルエーテル２００部に溶かし、これにスチレン５０部、２−エチルヘキシルメタクリレート２００部、ｎ−ブチルアクリレート３１３部、メタクリル酸７７部、プラクセルＦＭ−１（ダイセル社製水酸基含有重合性単量体）２６０部およびｔ−ブチルパーオキシ−２−ヘキサノエート８部を混合することによりモノマー溶液を別途調製した。このモノマー溶液を反応容器に撹拌下、３時間かけて滴下した後、３０分間撹拌を継続し、更にｔ−ブチルパーオキシ−２−エチルヘキサノエート５部とプロピレングリコールメチルエーテル５０部との混合液を１５分間で滴下した後、１時間攪拌を継続し、樹脂固形分が５９％、数平均分子量１３０００、水酸基価６０および酸価５０ｍｇＫＯＨ／ｇのアミド基含有アクリル樹脂１を得た。
【０１０３】
このアクリル樹脂５００部を、樹脂固形分が７５％になるまで脱溶剤し、ジメチルエタノールアミン２３．４部、イオン交換水９２５部を加えて、樹脂固形分が２２％の水溶性アミド基含有アクリル樹脂１を得た。
【０１０４】
塗膜形成性樹脂の製造２
窒素導入管、撹拌機、温度調節機、滴下ロートおよび冷却管を備えた１Ｌの反応容器にジプロピレングリコールメチルエーテル２３．８９部及びプロピレングリコールメチルエーテル１６．１１部を加え、窒素気流中で混合撹拌しながら１０５℃に昇温した。次いで、メタクリル酸メチル１３．１部、アクリル酸エチル６８．４部、メタクリル酸２−ヒドロキシエチル１１．６部、メタクリル酸６．９部と、ジプロピレングリコールメチルエーテル１０．０部及びｔ−ブチルパーオキシ２−エチルヘキサノエート１部からなる開始剤溶液とを３時間にわたり並行して反応容器に滴下した。滴下終了後、０．５時間同温度で熟成を行った。
【０１０５】
さらに、ジプロピレングリコールメチルエーテル５．０部及びｔ−ブチルパーオキシ２−エチルヘキサノエート０．３部からなる開始剤溶液を０．５時間にわたり反応容器に滴下した。滴下終了後、２時間同温度で熟成を行った。得られた樹脂溶液の不揮発分は３０．０％、固形分酸価４０ｍｇＫＯＨ／ｇ、水酸基価５０であった。
【０１０６】
脱溶剤装置により、減圧下（７０ｔｏｒｒ）１１０℃で溶剤を１６．１１部留去した後、イオン交換水２０４部及びジメチルエタノールアミン７．１４部を加えて水溶性アクリル樹脂２を得た。
【０１０７】
アクリル系ポリカルボン酸の合成
温度計、撹拌機、冷却管、窒素導入管、滴下ロートを備えた３Ｌの反応槽にキシレン７００重量部、ソルベッソ１００（エッソ社製芳香族炭化水素系溶剤）３５０重量部を仕込み、１３０℃に昇温して保持した。
【０１０８】
一方、スチレンモノマー３００重量部、メタクリル酸２−エチルヘキシル１０９重量部、アクリル酸イソブチル３２５重量部、アクリル酸２６重量部、無水マレイン酸２４０重量部、プロピレングリコールモノメチエーテルアセテート３００重量部、およびｔ−ブチルパーオキシ２−エチルヘキサノエイト１５０重量部及びキシレン１５０重量部からなる溶液を調製し、滴下ロートから上記反応槽内に３時間かけて滴下した。
【０１０９】
滴下終了後３０分間にわたり１３０℃で保持した後、ｔ−ブチルパーオキシ２−エチルヘキサノエイト２０重量部及びキシレン２０重量部からなる溶液を３０分間で滴下した。この滴下終了後、さらに１時間１３０℃にて反応を継続させ、その後溶剤を１１００重量部脱溶剤して、数平均分子量２０００のアクリル系ポリ酸無水物を含む不揮発分７０重量％のワニスを調製した。
【０１１０】
得られたワニス１５９０重量部に、メタノール１２５重量部を加え、７０℃で２３時間反応させ、酸価１５８ｍｇＫＯＨ／ｇ（固形分）のアクリル系ポリカルボン酸を得た。
【０１１１】
尚、このアクリル系ポリカルボン酸について赤外線吸収スペクトルを測定し、酸無水物基の吸収（１７８５ｃｍ^−１）が消失するのを確認した。
【０１１２】
ポリエステルポリカルボン酸の合成
温度計、撹拌機、冷却管、窒素導入管を備えた３Ｌの反応槽に３−エトキシプロピオン酸エチル２７８重量部、トリメチロールプロパン２６８重量部、ε−カプロラクトン２２８重量部、酸化ジブチルスズ０．１重量部を仕込み、１５０℃に昇温して保持した。
【０１１３】
２時間にわたり１５０℃で保持した後、加温して溶解したヘキサヒドロ無水フタル酸６１６重量部を加え、１５０℃で１時間保持して、数平均分子量８００、重量平均分子量／数平均分子量＝１．１８、酸価２０２ｍｇＫＯＨ／ｇ（固形分）及び水酸基価１０１ｍｇＫＯＨ／ｇ（固形分）のポリエステルポリカルボン酸を含む不揮発分８０重量％のワニスを得た。
【０１１４】
ポリエポキシドの合成
温度計、撹拌機、冷却管、窒素導入管、滴下ロートを備えた２Ｌの反応槽にキシレン２５０重量部、プロピレングリコールモノメチルエーテルアセテート２００重量部を仕込み、１３０℃に昇温して保持した。
【０１１５】
一方、メタクリル酸グリシジル４５０重量部、メタクリル酸イソボルニル２３６重量部、アクリル酸４−ヒドロキシブチル６４重量部、ｔ−ブチルスチレン２５０重量部、ｔ−ブチルパーオキシ２−エチルヘキサノエイト１１０重量部及びキシレン１５０重量部からなる溶液を調製し、滴下ロートから上記反応槽内に３時間かけて滴下した。溶液温度は１３０℃に保持した。
【０１１６】
滴下終了後３０分間にわたり１３０℃で保持した後、ｔ−ブチルパーオキシ２−エチルヘキサノエイト１０重量部及びキシレン５０重量部からなる溶液を３０分間で滴下した。この滴下終了後、さらに１時間１３０℃にて反応を継続させ、その後溶剤を２７０重量部脱溶剤して、数平均分子量２２００、エポキシ当量３１６及び水酸基価２５ｍｇＫＯＨ／ｇ（固形分）のアクリル系ポリエポキシドを含む不揮発分７２重量％のワニスを得た。
【０１１７】
実施例１
水性ベース塗料の調整
先の製造例で得られた水溶性アミド基含有アクリル樹脂１を１６４部、先の製造例で得られた水溶性アクリル樹脂２を８０部及びアルミニウム顔料ペースト「アルミペースト　ＭＨ−８８０１」（旭化成社製）１９部を加えて均一分散し、更に、メラミン樹脂「サイメル２０２」（三井サイテック社製）５０部、架橋性樹脂粒子（日本ペイント社製、動的光散乱法による平均粒径５５ｎｍ、固形分２０％、キシレン溶液）１０部、ジメチルエタノールアミン（沸点１３５℃、半当量電位点−１５ｍＶ）２１．３部（５．０当量になるように添加した。）とを加えてさらに均一分散することにより水性ベース塗料１を得た。尚、アクリル樹脂及びメラミン樹脂の配合量（部）は、固形分で表示した。
【０１１８】
次いで、イオン交換水を希釈媒体として用いて５０秒（Ｎｏ．４フォードカップを使用し、２０℃で測定）に希釈した。得られた希釈済み水性ベース塗料１は、固形分２４％であった。
【０１１９】
また、得られたベース塗料の硬化開始時間を、自由減衰振動型粘弾性測定装置（以下、「ＦＤＯＭ」と称する）により測定し、塗膜温度が所定焼き付け温度に達した時間をゼロ（±０）として、振動周期測定値のプロットより求めた減少開始時間を、反応開始時間として求めた。
【０１２０】
具体的に反応開始時間の測定は、オリエンテック社製剛体振り子型物性試験機「ＤＤＶ−ＯＰＡＩＩＩ」を用いて、金属支持体上に乾燥ベース膜厚が、１２μｍになるように塗料を塗布し、温度２５℃、６０％ＲＨの室内で３分間セッティングした後、塗膜の昇温を１分後に３０℃、３０℃から１０分後に１４０℃になるように昇温させ、１４０℃で２０分間保持する条件で行った。尚、反応開始時間は、ベース塗膜の温度が１４０℃に達した点を±０．０分とした。得られたベース塗料１の硬化開始時間は、１１．２分であった。
【０１２１】
ハイソリッド型クリヤー塗料の調製
上記により合成されたアクリル系ポリカルボン酸ワニスと、ポリエステルポリカルボン酸ワニス及びアクリル系ポリエポキシドワニスを、それぞれ不揮発分で２４重量部：２５重量部：５１重量部となるように混合し、テトラブチルアンモニウムブロミド硬化触媒０．５重量部、ジブチルスズビス（ブチルマレート）触媒０．５重量部、紫外線吸収剤（「チヌビン９００」チバガイギー社製）２重量部、光安定剤（「サノールＬＳ−４４０」三井社製）１重量部及び表面調整剤（「モダフロー」）０．１重量部をディスパー撹拌しながら混合した。得られた塗料のカルボキシル基／エポキシ基の当量比は、１００／９６であった。
【０１２２】
得られた塗料を３−エトキシプロピオン酸エチル／Ｓ−１５０（エッソ社製）＝１／１からなるシンナーにて、塗装粘度（フォードカップＮＯ．４、２０℃で３５秒）に希釈し、ハイソリッド型クリヤー塗料を調製した。この塗料０．５±０．１ｇを精秤し、１１０±５℃で６０分乾燥後の塗料の質量を精秤し、乾燥前の塗料の質量で割った値を１００倍して算出した不揮発分は５６．０重量％であり、ＶＯＣは４４０ｇ／ｌであった。
【０１２３】
また、得られたクリヤー塗料の硬化開始時間を、ベース塗料と同様の手法で「ＦＤＯＭ」により測定した。具体的に反応開始時間の測定は、オリエンテック社製剛体振り子型物性試験機「ＤＤＶ−ＯＰＡＩＩＩ」を用いて、クリヤー塗膜は４０μｍになるように塗布し、測定した。得られたクリヤー塗料の硬化開始時間は、１２．０分であった。
【０１２４】
塗膜形成方法
３０ｃｍ×４０ｃｍ、厚み０．８ｍｍの２枚のダル鋼板をリン酸亜鉛処理した後、カチオン電着塗料「パワートップＶ−６」（日本ペイント社製）及び中塗り塗料「オルガＰ−２グレー」（日本ペイント社製）を塗布された基材に、先の予め希釈された水性ベース塗料を、乾燥膜厚１５μｍとなるように外部印可型の「メタベル」を用い、印可電圧−６０ｋＶ、回転数２５０００ｒｐｍ、シェービングエアー圧３．５ｋｇ／ｃｍ^２、吐出量１２０ｃｃ／分で２ステージ塗装した。２回の塗布の間に、１．５分間のインターバルを行った。２回目の塗布後、３分間セッティングを行った後、８０℃で３分間プレヒートを行った。
【０１２５】
次に、上記で得られた水性ベース塗装板に、先の製造例のハイソリッド型クリヤー塗料を、乾燥膜厚４０μｍとなるように「マイクロマイクロベル」を用いて、印可電圧−９０ｋＶ、回転数３００００ｒｐｍ、シェービングエアー圧１．５ｋｇ／ｃｍ^２、吐出量２８０ｃｃ／分で、１ステージ塗装し、７分間セッティングした。次いで、得られた２枚の塗装板を、それぞれ１２０℃と１４０℃との乾燥機で２０分間焼付けを行った。
【０１２６】
得られた１４０℃焼き付けにより得られた塗装板について、塗膜外観、特に艶感について以下の評価基準により目視評価した。
＜艶感判断基準＞
５；非常に艶がよい
４；艶がよい
３；艶はある
２；若干艶が落ちる
１；艶感がない
【０１２７】
また、１２０℃と１４０℃との焼付けにより得られた２枚のメタリック塗膜を２４時間放置した後、８０℃の高温水に３時間浸せきした。引き上げた後に、カッターナイフにより２ｍｍの１００個の碁盤目を、素地に達するように作成し、テープによる剥離法により付着性を評価した。１００個の碁盤目の内、剥がれなかった碁盤目の升目の数を表記して付着性の結果とした。
結果を表１に示す。
【０１２８】
実施例２〜４、比較例１〜３
表１に示す３級アミンによって、水性メタリックベース塗料の製造に用いられる塗膜形成性樹脂のカルボキシル基を表示の当量比で中和し、実施例１と同様に各塗料を作成し、各塗料の硬化開始時間を測定した。また、同様に積層塗板を作成し評価した。結果を表１に示した。
【０１２９】
【表１】

【０１３０】
表１の結果より、本発明の塗膜形成方法によれば、外観の優れた積層塗膜を得ることができた。また特に、低温で焼付け硬化させた塗膜においても、高温耐水試験において、層間剥離することのない優れた塗膜を形成することができた。
【０１３１】
一方、比較例において、低沸点の３級アミンを含有するベース塗料を用いた系は外観が低下し、塩基性度の低いものは塗膜の硬化性を低下させたものと思われ、耐水付着性が低下した。
【０１３２】
【発明の効果】
すなわち本発明の塗膜形成方法によれば、２コート１ベーク塗装法においても、ベース塗膜の硬化速度は、含有される３級アミンの塩基性度により支配され、隣接するカルボン酸・エポキシ硬化系クリヤーの硬化速度は、ベース塗膜から移行した３級アミンの求核性に支配されたため、各塗膜の硬化バランスが最適になり、きわめて高品質の塗膜外観を有する積層塗膜を形成することができたものと思われる。すなわち、焼き付け時の３級アミンの移行は、本クリヤーの安定性を損ねることなく、クリヤーの架橋を十分に進行させることより塗膜性能が向上したものと思われる。
【０１３３】
すなわち、この手法により、ベース塗膜／クリヤー塗膜間の硬化速度差を効率よく、効果的に近づけることができるため、各層の硬化速度の違いにより発生する硬化歪みに起因する仕上がり外観の低下を抑制し、他の性能に悪影響を与えることなく、極めて高い仕上がり外観を達成することができたものである。
【０１３４】
また、実施例で用いたハイソリッド型クリヤー塗料はＶＯＣが低く、塗装粘度における不揮発分が高いので、揮発する有機溶剤量が少なく排気処理工数を低減することができる上、トリアジン環を含まないため酸性雨に対して大きな耐性を示し、自動車の上塗り塗装に最適である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a carboxylic acid / epoxy group-cured high solid type clear coating film on an aqueous base coating film by a two-coat one-bake coating method.
[0002]
[Prior art]
As a top coating for automobiles, there is a method of forming a coating film by a two-coat one-bake coating method. First, a base paint is applied, and after setting for a predetermined time, a clear paint is applied to the surface. Thereafter, the base coating film and the clear coating film are simultaneously baked and cured by heating. The thus-obtained laminated coating film is excellent in gloss, depth and the like, and is used as a top coat for automobiles.
[0003]
However, the base paint often contains a large amount of an organic solvent, and there is a concern about the effect on the environment. However, the aqueous base paint contains a basic component to make the film-forming resin aqueous. As a result, the coating film performance may be reduced or the curability may be affected.
[0004]
On the other hand, a conventional clear coating using a melamine resin as a curing agent has a low nonvolatile content of 30 to 45% by weight at the time of coating, so that a large amount of organic solvent is volatilized at the time of coating or baking and curing, and the number of processing steps is large. However, the acid resistance cannot be said to be high due to the presence of the triazine ring, and improvement in resistance to acid rain is also required.
[0005]
For example, JP-A-8-259667 discloses a resin composition containing a carboxyl group-containing resin and a polyepoxide. Since the resin liquid containing the resin composition has a high concentration and a low viscosity, the coating using the resin composition is a high solid coating. That is, when this high solid paint is used, the amount of volatile organic solvent can be suppressed, and since there is no triazine ring in the coating film, it is excellent in acid rain resistance.
[0006]
However, high-solid paints generally have a high concentration using a low-molecular-weight resin, so that during application or curing, the interface with the uncured base coating tends to blend in or mix, and the appearance of the paint depends on the coating conditions. May lead to a decline.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for forming a coating film in which an aqueous base coating material and a clear coating material are applied in two coats and one bake. To provide.
[0008]
[Means for Solving the Problems]
The method for forming a coating film of the present invention is a method for forming a two-coat one-bake coating film in which an aqueous base coating material and a clear coating material are sequentially applied on a substrate by wet-on-wet; Contains a tertiary amine having a half-equivalent point potential of −60 to 0 mV in a potentiometric titration and a boiling point of 120 to 290 ° C. in an amount of 1.5 to 7.0 equivalents of the carboxyl group of the carboxyl group-containing resin. And the clear paint is a carboxylic acid / epoxy group-curable paint, and a high solid type clear paint having a VOC of 400 to 550 in a diluted paint diluted to a coating viscosity. Is to provide.
[0009]
Further, the method of the present invention further comprises, as the carboxyl group-containing resin, an acrylic resin containing a carboxyl group and an amide group, and the acrylic resin containing the carboxyl group and the amide group, and another carboxyl group-containing resin. Is to provide a method for forming a coating film, wherein the weight ratio of the solid content is 30/70 to 90/10.
[0010]
Still another object is to provide a laminated coating film formed by the above method.
Hereinafter, the components of the present invention will be described in detail.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Aqueous base paint In the coating film forming method of the present invention, the aqueous base paint forms an overcoat film together with the clear paint. This coating composition contains a carboxyl group-containing resin and a tertiary amine having a half-equivalent point potential of −60 to 0 mV in a potentiometric titration and a boiling point of 120 to 290 ° C. It contains 0.5 to 7.0 equivalents, but may further contain a curing agent, a coloring pigment, and if necessary, a glittering pigment.
[0012]
The carboxyl group-containing resin preferably has an acid value of 2 to 80 mgKOH / g, more preferably 3 to 65 mgKOH / g. Exceeding the upper limit lowers the water resistance of the coating film, while lowering the lower limit lowers the curability of the coating film.
[0013]
Furthermore, it is particularly preferred that it has a hydroxyl value of 20 to 180, more preferably 30 to 160. Exceeding the upper limit lowers the water resistance of the coating film, while lowering the lower limit lowers the curability of the coating film.
[0014]
The carboxyl group-containing resin preferably has a number average molecular weight of 5,000 to 30,000, more preferably 7000 to 25,000. If it is less than 5000, workability and curability are not sufficient, and if it exceeds 30,000, the non-volatile content at the time of coating is too low, and the workability is rather reduced. In this specification, the molecular weight is determined by a GPC method using a styrene polymer as a standard.
[0015]
The carboxyl group-containing resin is not particularly limited, but preferred examples include an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, and a urethane resin. These can be used alone or in combination of two or more, but it is particularly preferable to use an acrylic resin having a carboxyl group from the viewpoint of weather resistance and pigment dispersibility.
[0016]
In order to produce the carboxyl group-containing acrylic resin, a carboxyl group-containing ethylenically unsaturated monomer and other ethylenically unsaturated monomers are used. The carboxyl group-containing ethylenically unsaturated monomer has a ratio of 0.1 to 10% by weight, preferably 0.5 to 8% by weight, based on the total amount of the polymerizable monomer for producing the carboxyl group-containing acrylic resin. And can be synthesized. When the content of the carboxyl group-containing ethylenically unsaturated monomer is less than 0.1% by weight, the stability of the coating composition is reduced. If it exceeds 10% by weight, the water resistance of the resulting coating film will be reduced.
[0017]
Examples of the ethylenically unsaturated monomer having a carboxyl group include (meth) acrylic acid derivatives (for example, ε-caprolactone added to acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, acrylic acid dimer and acrylic acid). Α-hydro-ω-((1-oxo-2-propenyl) oxy) poly (oxy (1-oxo-1,6-hexanediyl)) and the like; and unsaturated dibasic acids, half esters thereof ( For example, maleic acid, fumaric acid, itaconic acid, and half esters thereof and the like can be mentioned.
[0018]
Examples of the other ethylenically unsaturated monomers include, but are not particularly limited to, a hydroxyl group-containing ethylenically unsaturated monomer. Specifically, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, allyl alcohol and methacryl alcohol, 2-hydroxyethyl (meth) acrylate and ε-caprolactone And the like. Among them, it is preferable to use a long-chain hydroxyl group-containing monomer as the hydroxyl group-containing monomer from the viewpoint of improving chipping resistance. For example, adducts of 4-hydroxybutyl (meth) acrylate or 2-hydroxyethyl (meth) acrylate with ε-caprolactone, and the like can be given.
[0019]
Further, examples other than the above monomers include (meth) acrylate ester monomers (for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl (Meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, and dihydrodicyclopentadienyl (meth) acrylate ), Polymerizable aromatic compounds (eg, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, polymerizable nitriles (eg, acrylonitrile and methacrylonitrile). Yl), α-olefins (eg, ethylene and propylene), vinyl esters (eg, vinyl acetate and vinyl propionate), and dienes (eg, butadiene and isoprene). The saturated monomers can be used alone or in combination of two or more.
[0020]
A carboxyl group-containing acrylic resin can be obtained by radical copolymerization of each of the above ethylenically unsaturated monomers. As a polymerization method, an ordinary method described in known literature such as solution radical polymerization can be used. For example, a method in which an appropriate radical polymerization initiator and a monomer mixture solution are dropped into an appropriate solvent at a polymerization temperature of 60 to 160 ° C. for 2 to 10 hours while stirring is used. The radical polymerization initiator that can be used here is not particularly limited as long as it is usually used at the time of polymerization, and examples thereof include an azo compound and a peroxide. The solvent that can be used here is not particularly limited as long as it does not adversely affect the reaction, and examples thereof include alcohols, ketones, and hydrocarbon solvents. Further, in order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used if necessary.
[0021]
Further, as the carboxyl group-containing resin, in addition to the carboxyl group, further contains an amide group-containing carboxyl group and an amide group-containing acrylic resin, and the carboxyl group and amide group-containing acrylic resin and other carboxyl groups. The weight ratio of the solid content to the group-containing resin is more preferably 30/70 to 90/10. If the compounding ratio of the acrylic resin containing a carboxyl group and an amide group is below the lower limit, sagging is suppressed and the appearance is reduced, and if it exceeds the upper limit, the film forming property is deteriorated. More preferably, it is 50/50 to 80/20.
[0022]
In order to produce the acrylic resin containing a carboxyl group and an amide group, a carboxyl group-containing ethylenically unsaturated monomer, an amide group-containing ethylenically unsaturated monomer, and other ethylenically unsaturated monomers are used.
[0023]
The amide group-containing ethylenically unsaturated monomer is a carboxyl group-containing ethylenically unsaturated monomer based on the total amount of polymerizable monomers for producing an acrylic resin containing a carboxyl group and an amide group. The ethylenically unsaturated monomer is blended at 1 to 20% by weight, preferably 5 to 15% by weight. Further, the remaining amount and other ethylenically unsaturated monomers are used.
[0024]
When the content of the amide group-containing ethylenically unsaturated monomer is less than 1% by weight, the viscosity controllability and chipping resistance decrease. If it exceeds 20% by weight, the water resistance of the resulting coating film will be reduced.
[0025]
The number average molecular weight, acid value and hydroxyl group content of the acrylic resin containing a carboxyl group and an amide group are preferably in the ranges described for the acrylic resin containing a carboxyl group.
[0026]
Examples of the amide group-containing ethylenically unsaturated monomer include (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N -Dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide and the like. Preferred amide group-containing ethylenically unsaturated monomers are acrylamide, methacrylamide, N-monobutylacrylamide, and N-monobutylmethacrylamide.
[0027]
On the other hand, in order to make the carboxyl group-containing resin aqueous, the carboxyl group contained in the resin is neutralized with a basic component. A tertiary amine is used as the basic component. The half-equivalent point potential in the potentiometric titration of this tertiary amine is −60 to 0 mV, and the boiling point is 120 to 290 ° C. When the half-equivalent point potential exceeds the upper limit, the basicity is too low to exert an effect on improving the finish of the base coating film, and when the half-equivalent point potential is less than the lower limit, the basicity is too high and the curability of the base coating film is reduced. Preferably, the half-equivalent point potential in potentiometric titration is from -60 to -10 mV. If the boiling point exceeds the upper limit, amine remaining in the base coating film may cause curing inhibition, and the appearance may be reduced. If it is less than 10%, it will volatilize during painting and will not remain in the coating film until baking, resulting in a small effect. Preferably, the boiling point is from 130 to 250 ° C.
[0028]
The tertiary amine is used in an amount of 1.5 to 7.0 equivalents to the carboxyl group of the film-forming resin. If the amount of the tertiary amine is less than the lower limit, the storage stability of the coating material is reduced, and if it is more than the upper limit, the yellowing of the coating film is reduced. More preferably, it is used at 2.0 to 6.0 equivalents. The half-equivalent point potential of the tertiary amine in potentiometric titration is the half-equivalent point potential (mV) obtained by potentiometric titration with p-toluenesulfonic acid in an isopropanol solution, and is a measure of base strength. Is used.
[0029]
Specific examples of the tertiary amine include alkanolamines such as dimethylethanolamine (half-equivalent point potential of −15 mV, boiling point of 135 ° C.) and diethylethanolamine (half-equivalent point potential of −35 mV, boiling point of 161 ° C.), dimethylcyclohexylamine ( Alicyclic amines such as a half-equivalent point potential of -16 mV and a boiling point of 180 ° C., dicyclohexylmethylamine (a half-equivalent point potential of −58 mV and a boiling point of 260 ° C.), and tripropylamine (half-equivalent point potential of −25 mV and a boiling point of 157 ° C.); Aliphatic amines such as tributylamine (half-equivalent point potential: -40 mV, boiling point: 214 ° C.);
[0030]
Among the above, dimethylethanolamine having a boiling point of 130 to 250 ° C (half equivalent point potential −15 mV, boiling point 135 ° C), diethylethanolamine (half equivalent point potential -35 mV, boiling point 161 ° C), dimethylcyclohexylamine (half equivalent point) Potential -16 mV, boiling point 180 ° C.), tripropylamine (half equivalent point potential −25 mV, boiling point 157 ° C.), tributylamine (half equivalent point potential −40 mV, boiling point 214 ° C.) It is possible to create a multilayer coating film with excellent balance and excellent appearance.
[0031]
Preferred examples of the curing agent include an amino resin, a blocked isocyanate resin, an epoxy compound, an aziridine compound, a carbodiimide compound, and an oxazoline compound. An amino resin and / or a blocked isocyanate resin are particularly preferably used in view of various properties and cost of the obtained coating film.
[0032]
The content of the curing agent is 20 to 100% by weight based on the solid content of the film-forming resin component including the carboxyl group-containing resin and other resins. If the content is less than 20% by weight, the curability becomes insufficient, and if it exceeds 100% by weight, the cured film becomes too hard and brittle.
[0033]
The amino resin as the curing agent is not particularly limited, and a methylated melamine resin, a butylated melamine resin, or a mixed melamine resin of methyl and butyl can be used. For example, "Symer-303", "Symel 254", "Uban 20N60" commercially available from Mitsui Toatsu Co., Ltd., and "Sumimar Series" commercially available from Sumitomo Chemical Co., Ltd. are exemplified.
[0034]
Examples of the coloring pigment include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylene pigments. Pigments, dioxane-based pigments, quinacridone-based pigments, isoindolinone-based pigments, metal complex pigments, and the like can be mentioned. Inorganic-based pigments include graphite, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. As the extender pigment, calcium carbonate, barium sulfate, clay, talc and the like are used.
[0035]
The glitter pigment is not particularly limited in its shape and may be further colored. For example, the glitter pigment has an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm and a thickness of 0.1 to 5 μm. Are preferred. Those having an average particle size in the range of 10 to 35 μm are excellent in glitter and are more preferably used.
[0036]
The pigment concentration (PWC) of the brilliant pigment in the paint is generally 20.0% or less. If it exceeds the upper limit, the appearance of the coating film will be reduced. Preferably, it is 0.01% to 18.0%, more preferably 0.1% to 15.0%. When the content of the glittering agent exceeds 20.0% by weight, the appearance of the coating film is deteriorated.
[0037]
Examples of the glitter pigment include non-colored or colored metal glitters such as metals or alloys such as aluminum, copper, zinc, iron, nickel, tin and aluminum oxide, and mixtures thereof. Further, interference mica pigments, white mica pigments, graphite pigments and other colored or colored flat pigments may be used.
[0038]
The total pigment concentration (PWC) in the paint including the glitter pigment and all other pigments is 0.1 to 50%, preferably 0.5% to 40%, more preferably , 1.0% to 30%. If it exceeds the upper limit, the appearance of the coating film will be reduced.
[0039]
Furthermore, it is preferable to add a viscosity control agent to the aqueous base paint, as in the above-described intermediate paint, in order to ensure coating workability. The viscosity controlling agent is used for favorably forming a coating film without unevenness and sagging, and generally contains a material having a thixotropic property. Preferably, crosslinked or non-crosslinked resin particles are used.
[0040]
The aqueous base paint used in the present invention contains, in addition to the above components, additives usually added to the paint, such as a surface conditioner, a thickener, an antioxidant, an ultraviolet ray inhibitor, an antifoaming agent, and the like. May be. These amounts are within the range known to those skilled in the art.
[0041]
The total solid content of the aqueous base paint used in the present invention at the time of coating is 10 to 60% by weight, preferably 15 to 50% by weight. Exceeding the upper and lower limits lowers the paint stability. If it exceeds the upper limit, the viscosity is too high and the appearance of the coating film is reduced. If it is below the lower limit, the viscosity is too low and poor appearance such as adaptability and unevenness occurs.
[0042]
Clear coating The clear coating used in the present invention is a carboxylic acid / epoxy group-curable coating, and is a high solid type clear coating having a VOC of 400 to 550 in a diluted coating diluted to the coating viscosity.
[0043]
As the carboxylic acid / epoxy group-curable high solid type clear coating, those which form an ester bond formed by a reaction between a carboxyl group and an epoxy group by heating are preferably used, and specifically as a resin component. Examples include those containing a carboxyl group-containing resin and a polyepoxide.
[0044]
As the carboxyl group-containing resin, (a) an acrylic polycarboxylic acid having an average of two or more carboxyl groups in one molecule, an acid value of 5 to 300 mg KOH / g (solid content), and a number average molecular weight of 500 to 8000 An acid value of 50 to 350 mgKOH / g (solid content) obtained by reacting 10 to 70 parts by weight, (b) a polyester polyol having three or more hydroxyl groups with an acid anhydride, a number average molecular weight of 400 to 3500, and It is desirable to use a polyester polycarboxylic acid having a weight average molecular weight / number average molecular weight of 1.8 or less by 5 to 70 parts by weight.
[0045]
As the acrylic polycarboxylic acid (a), a carboxyl group and a carboxylic ester group obtained by reacting (1) an acrylic polyanhydride with (2) a monoalcohol bond to adjacent carbon. It is desirable to use an acrylic polycarboxylic acid.
[0046]
(A)-(1) An acrylic polyanhydride is an ethylenically unsaturated monomer having no acid anhydride group, having 15 to 40% by weight, preferably 15 to 35% by weight of an ethylenically unsaturated monomer containing an acid anhydride group. It is obtained by copolymerizing 60 to 85% by weight, preferably 65 to 85% by weight of a saturated monomer. If the amount of the acid anhydride group-containing ethylenically unsaturated monomer is less than 15% by weight, the curability will be insufficient, and if it exceeds 40% by weight, the coating film will be too hard and brittle, and the weather resistance will be insufficient.
[0047]
Examples of the acid anhydride group-containing ethylenically unsaturated monomer include itaconic anhydride, maleic anhydride, and citraconic anhydride.
[0048]
The ethylenically unsaturated monomer having no acid anhydride group is not particularly limited as long as it is an ethylenically unsaturated monomer that does not adversely affect the acid anhydride group, but has 3 to 3 carbon atoms having one ethylenically unsaturated bond. It is preferred to use 15, especially 3 to 12, monomers.
[0049]
It is also preferable to use two or more ethylenically unsaturated monomers having no acid anhydride group in order to improve the compatibility between the resins.
[0050]
Examples of such ethylenically unsaturated monomers having no acid anhydride group include styrene, α-methylstyrene, pt-butylstyrene, various (meth) acrylic esters, VeoVa-9 and VeoVa manufactured by Shell. And versatic acid glycidyl ester such as -10. When styrene or a styrene derivative is used, it is desirable to use styrene or a styrene derivative in the range of 5 to 40% by weight based on all monomers.
[0051]
Further, as an ethylenically unsaturated monomer having no acid anhydride group, a monomer having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid and maleic acid, and an ethylenically unsaturated monomer having a hydroxyl group and an acid anhydride group Adducts with the containing compounds can also be used. Among them, it is particularly preferable to use a long-chain carboxyl group-containing monomer having a spacer portion of about 5 to 20 carbon atoms between the ethylenically unsaturated group and the carboxyl group because the scratch resistance of the coating film is improved. .
[0052]
The number average molecular weight of the (a)-(1) acrylic polyanhydride obtained by copolymerizing an ethylenically unsaturated monomer having an acid anhydride group and an ethylenically unsaturated monomer having no acid anhydride group is 500 to 500. It is preferably 8000, 800 to 6000, and particularly preferably 1500 to 4000. When the number average molecular weight exceeds 8000, the compatibility between the resins decreases, and the appearance quality of the coating film deteriorates. When the number average molecular weight is less than 500, the curability becomes insufficient. It is desirable that the polymer obtained has an average of at least 2, preferably 2 to 15 acid anhydride groups in one molecule. If the number of acid anhydride groups is less than 2, the curability will be insufficient, and if it exceeds 15, the coating film will be too hard and brittle, and the weather resistance will be insufficient.
[0053]
As the (a)-(2) monoalcohol, it is preferable to use one having 1 to 12 carbon atoms, particularly 1 to 8 carbon atoms. This is because the alcohol easily volatilizes during the reaction with the acrylic polyanhydride, which is suitable for regenerating the acid anhydride group.
[0054]
Such monoalcohols include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-hexyl alcohol, lauryl alcohol, methyl cellosolve, ethyl cellosolve, methoxypropanol, ethoxy Examples thereof include propanol, furfuryl alcohol, dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, and propargyl alcohol.
[0055]
When (a)-(1) an acrylic polyanhydride is reacted with (a)-(2) a monoalcohol to synthesize (a) an acrylic polycarboxylic acid, the acid anhydride group and the hydroxyl group are in moles. The ratio is 1/10 to 1/1, preferably 1/5 to 1/1, more preferably 1/2 to 1/1. If the molar ratio is less than 1/10, excess alcohol may cause cracking at the time of curing, and if it exceeds 1/1, unreacted acid anhydride groups remain and storage stability deteriorates.
[0056]
The acrylic polycarboxylic acid (a) having a carboxyl group and a carboxylic ester group obtained by the above reaction preferably has an acid value of 5 to 300 mgKOH / g, particularly preferably 50 to 250 mgKOH / g. If the acid value is lower than 5 mgKOH / g, the curability will be insufficient, and if it is higher than 300 mgKOH / g, the storage stability will be poor.
[0057]
(A) The acrylic polycarboxylic acid is used in an amount of 10 to 70% by weight, preferably 15 to 50% by weight, more preferably 20 to 45% by weight, based on the total nonvolatile components in the resin composition. If the amount is less than 10% by weight, the weather resistance of the obtained coating film is reduced, and if it exceeds 70% by weight, the coating film becomes too hard.
[0058]
(B) Polyester polycarboxylic acid, which is another component of the carboxyl group-containing resin, is obtained by half-esterifying (1) a polyester polyol having three or more hydroxyl groups and (2) an acid anhydride. In addition, the polyester polyol refers to a polyhydric alcohol having two or more ester bond chains, and reacts with an acid anhydride group to form a polyester polycarboxylic acid having two or more acid functionalities per molecule and the following properties. .
[0059]
Such a (b)-(1) polyester polyol comprises a low molecular weight polyhydric alcohol having at least 3 hydroxyl groups and having 3 to 16 carbon atoms, or a lactone compound such as ε-caprolactone. It can also be synthesized by adding and extending the chain. By introducing a linear aliphatic group into the low molecular weight polyhydric alcohol, the obtained coating film is given flexibility and the impact resistance is improved.
[0060]
Examples of the low molecular weight polyhydric alcohol to be used include trimethylolethane, trimethylolpropane, 1,2,4-butanetriol, ditrimethylolpropane, pentaerythritol, dipentaerythritol, glycerin and mixtures thereof.
[0061]
Examples of preferably used low molecular weight polyhydric alcohols include trimethylolpropane, ditrimethylolpropane, pentaerythritol, and adducts of these with lactone compounds. Examples of the lactone compound include ε-caprolactone, γ-caprolactone, γ-valerolactone, δ-valerolactone, and γ-butyrolactone, and ε-caprolactone, γ-valerolactone, and γ-butyrolactone are preferred.
[0062]
Examples of (b)-(2) acid anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, trimellitic anhydride, succinic anhydride, and the like.
[0063]
The half esterification reaction between (b)-(1) polyester polyol and (b)-(2) acid anhydride can be carried out under ordinary reaction conditions such as room temperature to 150 ° C. and normal pressure. However, it is not necessary to modify all the hydroxyl groups of the polyester polyol to carboxyl groups, and the hydroxyl groups may be left. According to the above-described method, the molecular weight distribution becomes sharp, so that further high solidification is possible, and a coating film excellent in weather resistance and water resistance can be formed.
[0064]
The (b) polyester polycarboxylic acid obtained by the above reaction has an acid value of 50 to 350 mg KOH / g (solid content), preferably 100 to 300 mg KOH / g (solid content), and more preferably 150 to 250 mg KOH / g (solid content). ), The number average molecular weight is 400-3500, preferably 500-2500, more preferably 700-2000, and the weight average molecular weight / number average molecular weight is 1.8 or less, preferably 1.5 or less. Preferably it is 1.35 or less.
[0065]
When the acid value exceeds 350 mgKOH / g, the resin viscosity becomes too high, causing a decrease in the non-volatile content of the coating. When the acid value is lower than 50 mgKOH / g, the curability of the coating becomes insufficient. On the other hand, if the molecular weight exceeds 3500, the resin viscosity becomes too high, causing a decrease in the nonvolatile content of the diluted paint diluted to the coating viscosity, and if it is less than 400, the curability becomes insufficient. Further, when the weight average molecular weight / number average molecular weight exceeds 1.8, the water resistance and weather resistance of the coating film decrease.
[0066]
(B) Since the polyester polycarboxylic acid has a hydroxyl group in the molecule, a carboxyl group and a hydroxyl group are simultaneously provided on the surface of the coating film, for example, the adhesion at the time of recoating is improved. In this case, the hydroxyl value of the polyester polycarboxylic acid is preferably 150 mgKOH / g (solid content) or less, preferably 5 to 100 mgKOH / g (solid content), and more preferably 10 to 80 mgKOH / g (solid content). If the hydroxyl value exceeds 150 mgKOH / g (solid content), the water resistance will decrease.
[0067]
(B) Polyester carboxylic acid having a hydroxyl group and a carboxyl group reacts with both (c) polyepoxide and (a) acrylic polycarboxylic acid as described later, so that a stronger coating film can be formed. . Therefore, it is desirable that the polyester carboxylic acid (b) has an average of 0.1 or more hydroxyl groups in one molecule.
[0068]
In order to obtain such a polyester carboxylic acid, the molar amount of the acid anhydride group of (b)-(2) acid anhydride with respect to the molar amount of (b)-(1) polyester polyol is 0.2-1. It is preferably set to 0.0 times, especially 0.5 to 0.9 times. If this ratio is less than 0.2 times, the curability of the coating will be insufficient.
[0069]
(B) The polyester polycarboxylic acid component may be blended in an amount of 5 to 70% by weight, preferably 5 to 50% by weight, more preferably 10 to 40% by weight based on the weight of all non-volatile components in the paint. it can. (B) If the amount of the polyester polycarboxylic acid is less than 5% by weight, the non-volatile content of the coating does not increase, and if it exceeds 70% by weight, the weather resistance of the coating film decreases.
[0070]
The polyepoxide (c), which is another component of the high solid type clear coating used in the present invention, has an average of two or more, preferably 2 to 10, more preferably 3 to 8 epoxy groups in one molecule. Compound.
[0071]
Preferred as (c) polyepoxide are (1) 10 to 60% by weight, preferably 15 to 50% by weight, of an epoxy group-containing ethylenically unsaturated monomer, and (2) 40 to 40% by weight of an ethylenically unsaturated monomer having no epoxy group. Acrylic polyepoxide obtained by copolymerizing 90% by weight, preferably 50 to 85% by weight. If the amount of the epoxy group-containing ethylenically unsaturated monomer is less than 10% by weight, the curability will be insufficient, and if it is more than 60% by weight, it will be too hard and the weather resistance will be insufficient.
[0072]
Examples of the (c)-(1) epoxy group-containing ethylenically unsaturated monomer include glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, and 3,4-epoxycyclohexanyl (meth) acrylate. You. In order to ensure curability and storage stability, it is preferable to use glycidyl (meth) acrylate.
[0073]
(C)-(2) As the ethylenically unsaturated monomer having no epoxy group, the above-mentioned ethylenically unsaturated monomer having no acid anhydride group which does not affect the epoxy group may be used in the same manner. it can.
[0074]
The number average molecular weight of the acrylic polyepoxide obtained by copolymerization of the above monomers is from 500 to 10,000, preferably from 1,000 to 8,000, more preferably from 1500 to 5,000. If the number average molecular weight is less than 500, the curability of the coating will be insufficient, and if it exceeds 10,000, the nonvolatile content of the diluted coating diluted to the coating viscosity will decrease. The epoxy equivalent is 50 to 700, preferably 80 to 600, more preferably 100 to 500. If the epoxy equivalent exceeds 700, the curability of the coating becomes insufficient, and if it is less than 50, the coating becomes too hard and the coating film becomes brittle, which is not preferable.
[0075]
In addition, as the (c)-(2) ethylenically unsaturated monomer having no epoxy group, a hydroxyl group-containing ethylenically unsaturated monomer represented by Chemical Formula 1 can be used.
[0076]
Embedded image

(In the formula, R is a hydrogen atom or a methyl group, and X is an organic chain represented by Formula 2 or Formula 3.)
[0077]
Embedded image

(In the formula, Y is a linear or branched alkylene group having 2 to 8 carbon atoms, m is an integer of 3 to 7, and q is an integer of 0 to 4.)
[0078]
Embedded image

(In the formula, R is a hydrogen atom or a methyl group, and n is an integer of 2 to 50.)
[0079]
Specific examples of the hydroxyl group-containing ethylenically unsaturated monomer represented by Formula 1 include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and (meth). ) 4-Hydroxybutyl acrylate, 6-hydroxyhexyl (meth) acrylate, and their reactants with ε-caprolactone, (meth) acrylic acid and a large excess of diols (eg, 1,4 butanediol, 1,4 Compounds obtained by esterifying 6 hexanediol, polyethylene glycol, and polypropylene glycol) are exemplified.
[0080]
As the hydroxyl group-containing ethylenically unsaturated monomer used herein, those having 5 to 23 carbon atoms, particularly 5 to 13 carbon atoms, can be preferably used. If the chain length of the monomer is too short, the flexibility near the cross-linking point is lost, so that the monomer becomes too hard, and if it is too long, the molecular weight between the cross-linking points becomes too large.
[0081]
The use of the hydroxyl group-containing ethylenically unsaturated monomer improves the adhesion and recoating property of the resulting coating film. In addition, the acrylic polyepoxide having a hydroxyl group and a carboxyl group reacts with the (a) acrylic polycarboxylic acid having a carboxyl group and a carboxylic ester group in both functional groups of a hydroxyl group and an epoxy group, as described later. Because of the bonding, a stronger coating film can be obtained.
[0082]
The hydroxyl value of the acrylic polyepoxide is 5 to 300 mgKOH / g (solid content), preferably 10 to 200 mgKOH / g (solid content), and more preferably 15 to 150 mgKOH / g (solid content). When the hydroxyl value exceeds 300 mg KOH / g (solid content), the non-volatile content of the coating material decreases and the water resistance of the coating film becomes insufficient. When the hydroxyl value is less than 5 mg KOH / g (solid content), the adhesion is poor.
[0083]
The polyepoxide (c) suitable for use in the present invention comprises 5-70% by weight of a hydroxyl group-containing ethylenically unsaturated monomer having the structure represented by the above-mentioned formulas 1-3 and (c)-(1) an epoxy group-containing ethylene. It is obtained by copolymerizing 10 to 60% by weight of an ethylenically unsaturated monomer and optionally 0 to 85% by weight of an ethylenically unsaturated monomer having neither a hydroxyl group nor an epoxy group. In this case, the resulting polyepoxide (c) has an average of 2 to 12, more preferably 3 to 10 epoxy groups and an average of 0.5 to 10 hydroxyl groups, more preferably 1 to 8 epoxy groups in one molecule. Have
[0084]
(C) The polyepoxide component is blended in an amount of 10 to 80% by weight, preferably 20 to 70% by weight, more preferably 30 to 65% by weight, based on the weight of the total solids in the curable resin composition. Can be. If the amount of the polyepoxide is less than 10% by weight, the curability decreases, and if it exceeds 80% by weight, yellowing resistance deteriorates.
[0085]
The high solid type clear coating material referred to in the present invention can be produced by mixing three components of (a) an acrylic polycarboxylic acid, (b) a polyester polycarboxylic acid, and (c) a polyepoxide. Particularly when using (a) an acrylic polycarboxylic acid having a carboxyl group and a carboxylic ester group and using (c) a polyepoxide having a hydroxyl group and an epoxy group, a coating film having particularly excellent acid resistance is formed. A high solid type clear paint is obtained.
[0086]
In this case, the molar ratio of the carboxyl group contained in (a) the acrylic polycarboxylic acid and (b) the polyester polycarboxylic acid to the epoxy group contained in (c) the polyepoxide is 1 / 1.4 to 1 / 1.4. 0.6, preferably 1 / 1.2 to 1 / 0.8, and (a) a carboxylate group contained in the acrylic polycarboxylic acid or a carboxylate group bonded to the carbon adjacent to the carboxyl group-bonded carbon And the molar ratio of the hydroxyl groups contained in the (b) polyester polycarboxylic acid and the (c) polyepoxide is 1 / 2.0 to 1 / 0.5, more preferably 1 / 1.5 to 1 / 0.7. It is preferable to mix them in such amounts.
[0087]
Paint obtained when the molar ratio of the carboxyl group contained in (a) the acrylic polycarboxylic acid and (b) the polyester polycarboxylic acid to the epoxy group contained in (c) the polyepoxide exceeds 1 / 0.6. The curability of the film decreases, and when it is smaller than 1 / 1.4, the coating film turns yellow. Further, (a) a carboxyl group contained in the acrylic polycarboxylic acid or a carboxylate ester group bonded to the carbon adjacent to the carboxyl group-bonded carbon, and (b) a hydroxyl group contained in the polyester polycarboxylic acid and (c) the polyepoxide If the molar ratio exceeds 1 / 0.5, the curability of the resulting coating material will decrease, and if it is less than 1 / 2.0, the hydroxyl group will be excessive, and the water resistance will decrease.
[0088]
The curing mechanism of the thus obtained high solid type clear paint is as follows. First, the carboxyl group in the acrylic polycarboxylic acid reacts with the carboxylic ester group by heating, and An acid anhydride group is formed in the compound, and a free monoalcohol is formed. The produced monoalcohol evaporates and is removed out of the system. The acid anhydride groups formed in the (a) acrylic polycarboxylic acid react with the hydroxyl groups contained in the (b) polyester polycarboxylic acid and the (c) polyepoxide to form cross-linking points and form carboxyl groups again. Form. The carboxyl group and the carboxyl group present in (b) the polyester polycarboxylic acid form a crosslinking point by reacting with the epoxy group present in (c) the polyepoxide. As described above, the three types of polymers react with each other, whereby the curing proceeds, and a crosslinked coating film having a high density is formed.
[0089]
The high solid type clear coating composition referred to in the present invention may contain a curing catalyst usually used for an esterification reaction between an acid and an epoxy such as a quaternary ammonium salt. Examples of the curing catalyst include benzyltriethylammonium chloride or bromide, tetrabutylammonium chloride or bromide, salicylate or glycolate, and paratoluenesulfonate.
[0090]
The amount of the curing catalyst to be added is generally 0.01 to 3.0% by weight, preferably 0.1 to 1.5% by weight, more preferably 0.4 to 1.2% by weight based on the solid content of the resin composition. % By weight. If the amount of the curing catalyst is less than 0.01% by weight, the effect of the addition cannot be obtained, and if the amount exceeds 3.0% by weight, the storage stability decreases.
[0091]
In the high solid type clear coating composition according to the present invention, a tin compound disclosed in JP-A-2-151651 or the like can be mixed. Examples of such a tin-based catalyst include dimethyltin bis (methylmalate), dimethyltinbis (ethylmalate), dimethyltinbis (butylmalate), and dibutyltinbis (butylmalate).
[0092]
The amount of the tin-based catalyst to be added is generally 0.05 to 6.0% by weight, preferably 0.1 to 4.0% by weight, more preferably 0.2 to 2.0% by weight, based on the solid content of the resin composition. 0% by weight. If the amount of the tin-based catalyst is less than 0.05% by weight, the storage stability decreases, and if it exceeds 6.0% by weight, the weather resistance decreases. When a curing catalyst and a tin-based catalyst are used in combination, the weight ratio of the curing catalyst to the tin-based catalyst is preferably 1/4 to 1 / 0.2.
[0093]
In order to increase the crosslink density and improve the water resistance, a blocked isocyanate may be added to the high solid type clear coating composition according to the present invention. Further, a known ultraviolet absorber, light stabilizer, antioxidant and the like may be added. Furthermore, a known rheology control agent, a surface conditioner or the like may be added, or a solvent such as an alcohol-based solvent, an aromatic hydrocarbon-based solvent, an ester-based solvent, or a ketone-based solvent may be used for viscosity control or the like. it can.
[0094]
Coating film forming method In the coating film forming method of the present invention, two coats of an aqueous base coating material and a carboxylic acid / epoxy group-curable high solid type clear coating material having a VOC of 400 to 550 in a diluted coating material are used. Paint by bake coating method. When the VOC is less than 400, the surface smoothness of the formed coating film is reduced, and when it exceeds 550, it becomes difficult to secure a desired film thickness. Note that VOC is an abbreviation of Volatile Organic Compound, and is a value calculated by actually measuring the non-volatile content of a diluted paint and the specific gravity of the diluted paint and substituting it into the following equation. Generally, the higher the VOC, the lower the non-volatile content in the paint, and the lower the VOC, the higher the non-volatile content.
VOC = 1000 × Dilution paint specific gravity × (1−Dilution paint non-volatile content / 100)
[0095]
The state in which the solvent-type clear paint is diluted to the coating viscosity, the atomization method of the electrostatic coating machine described later, or the coating viscosity determined empirically based on factors such as the coating environment such as temperature and humidity, It shows a state where the viscosity has been adjusted by dilution with an organic solvent for dilution. Generally, the coating viscosity at a temperature of 15 ° C. to 40 ° C. and a humidity of 10% to 98% is preferably 20 to 50 seconds (/ 20 ° C. No. 4 Ford Cup). Outside of this range, appearance defects such as sagging and armpits are likely to occur. More preferably, it is 22 to 40 seconds (/ 20 ° C, No. 4 Ford cup).
[0096]
When applying the above water-based paint to an automobile body, it is generally applied by air spray coating, or a rotary atomization type electrostatic coating machine commonly called "bell", and after a predetermined time interval, the clear paint is applied. Painted.
[0097]
The aqueous base paint is generally applied in a range where the dry film thickness is 10 to 30 μm. When the thickness is larger than 30 μm or smaller than 10 μm, the appearance quality is deteriorated. The setting time after the application of the aqueous base paint is 3 to 15 minutes at room temperature as in the conventional case. If the setting time is shorter than 3 minutes, a burning may occur at the time of printing, and even if the setting time is 15 minutes or more, the effect is saturated and dust or the like adheres, which is not preferable. Further, preheating can be performed at 40 to 100 ° C. for about 3 to 15 minutes.
[0098]
The above-mentioned high solid type clear paint is generally applied in a range where the dry film thickness is 25 to 70 μm. If this film thickness is more than 70 μm, sagging will occur, and if it is less than 25 μm, the film thickness of the final coating film will be insufficient and the appearance quality will deteriorate.
[0099]
The setting time after application of the high solid clear paint is about 3 to 15 minutes. If the setting time is shorter than 3 minutes, armpits are likely to occur, and if the setting time is longer than 15 minutes, the effect is saturated and dust and the like adhere, which is not preferable.
[0100]
Thereafter, both wet coatings are heated to 100 to 180 ° C., preferably 120 to 160 ° C., and are baked and cured integrally to form coatings. The baking time varies depending on the temperature, but is suitably from 120 to 160 ° C. and from 10 to 30 minutes.
[0101]
【Example】
Hereinafter, the present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples. In the following, “parts” means “parts by weight”.
[0102]
Manufacturing example
Production of film-forming resin 1
450 parts of propylene glycol ethyl ether was charged into a 2 L reaction vessel equipped with a nitrogen introduction pipe, a stirrer, a temperature controller, a dropping funnel and a cooling pipe, and the temperature was adjusted to 107 ° C. Next, 100 parts of acrylamide was dissolved in 200 parts of propylene glycol methyl ether, and 50 parts of styrene, 200 parts of 2-ethylhexyl methacrylate, 313 parts of n-butyl acrylate, 77 parts of methacrylic acid, and Praxel FM-1 (a hydroxyl group manufactured by Daicel Corporation) (Containing polymerizable monomer) 260 parts and t-butyl peroxy-2-hexanoate 8 parts were mixed to separately prepare a monomer solution. This monomer solution was added dropwise to the reaction vessel over 3 hours with stirring, followed by stirring for 30 minutes, and further mixing of 5 parts of t-butyl peroxy-2-ethylhexanoate and 50 parts of propylene glycol methyl ether. After the liquid was added dropwise for 15 minutes, stirring was continued for 1 hour to obtain an amide group-containing acrylic resin 1 having a resin solid content of 59%, a number average molecular weight of 13,000, a hydroxyl value of 60 and an acid value of 50 mgKOH / g.
[0103]
500 parts of this acrylic resin is desolvated until the resin solid content becomes 75%, 23.4 parts of dimethylethanolamine and 925 parts of ion-exchanged water are added, and a water-soluble amide group-containing acrylic resin having a resin solid content of 22% is added. Resin 1 was obtained.
[0104]
Production of film-forming resin 2
23.89 parts of dipropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether are added to a 1 L reaction vessel equipped with a nitrogen inlet tube, a stirrer, a temperature controller, a dropping funnel and a cooling tube, and mixed in a nitrogen stream. The temperature was raised to 105 ° C. while stirring. Subsequently, 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate, 6.9 parts of methacrylic acid, 10.0 parts of dipropylene glycol methyl ether and t-butyl An initiator solution consisting of 1 part of peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of dropping, aging was performed at the same temperature for 0.5 hour.
[0105]
Further, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 parts of t-butylperoxy 2-ethylhexanoate was dropped into the reaction vessel over 0.5 hours. After completion of the dropwise addition, aging was performed at the same temperature for 2 hours. The obtained resin solution had a nonvolatile content of 30.0%, an acid value of solid content of 40 mgKOH / g and a hydroxyl value of 50.
[0106]
16.11 parts of the solvent was distilled off at 110 ° C. under reduced pressure (70 torr) by a solvent removing apparatus, and 204 parts of ion-exchanged water and 7.14 parts of dimethylethanolamine were added to obtain a water-soluble acrylic resin 2.
[0107]
Synthesis of acrylic polycarboxylic acid 700 parts by weight of xylene, Solvesso 100 (aromatic hydrocarbon system manufactured by Esso Co., Ltd.) in a 3 L reaction tank equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel. Solvent) (350 parts by weight) was charged, and the temperature was raised to 130 ° C. and maintained.
[0108]
On the other hand, 300 parts by weight of styrene monomer, 109 parts by weight of 2-ethylhexyl methacrylate, 325 parts by weight of isobutyl acrylate, 26 parts by weight of acrylic acid, 240 parts by weight of maleic anhydride, 300 parts by weight of propylene glycol monomethyl ether acetate, and t- A solution consisting of 150 parts by weight of butyl peroxy 2-ethylhexanoate and 150 parts by weight of xylene was prepared and added dropwise from the dropping funnel into the above reaction vessel over 3 hours.
[0109]
After maintaining at 130 ° C. for 30 minutes after completion of the dropwise addition, a solution comprising 20 parts by weight of t-butylperoxy 2-ethylhexanoate and 20 parts by weight of xylene was added dropwise over 30 minutes. After completion of the dropping, the reaction was further continued at 130 ° C. for 1 hour, and thereafter, 1100 parts by weight of the solvent was removed to prepare a varnish having a nonvolatile content of 70% by weight including an acrylic polyanhydride having a number average molecular weight of 2,000. did.
[0110]
To 1590 parts by weight of the obtained varnish, 125 parts by weight of methanol was added and reacted at 70 ° C. for 23 hours to obtain an acrylic polycarboxylic acid having an acid value of 158 mgKOH / g (solid content).
[0111]
The infrared absorption spectrum of this acrylic polycarboxylic acid was measured, and it was confirmed that the absorption (1785 cm ⁻¹ ) of the acid anhydride group disappeared.
[0112]
Synthesis of polyester polycarboxylic acid In a 3 L reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, and a nitrogen introducing pipe, 278 parts by weight of ethyl 3-ethoxypropionate, 268 parts by weight of trimethylolpropane, ε-caprolactone 228 parts by weight and 0.1 part by weight of dibutyltin oxide were charged, and the temperature was raised to 150 ° C. and maintained.
[0113]
After keeping at 150 ° C. for 2 hours, 616 parts by weight of hexahydrophthalic anhydride dissolved by heating are added, and the mixture is kept at 150 ° C. for 1 hour to give a number average molecular weight of 800, weight average molecular weight / number average molecular weight = 1. 18. A varnish having a non-volatile content of 80% by weight containing a polyester polycarboxylic acid having an acid value of 202 mg KOH / g (solid content) and a hydroxyl value of 101 mg KOH / g (solid content) was obtained.
[0114]
Synthesis of polyepoxide 250 parts by weight of xylene and 200 parts by weight of propylene glycol monomethyl ether acetate were charged into a 2 L reaction tank equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, and heated to 130 ° C. Warmed and held.
[0115]
On the other hand, 450 parts by weight of glycidyl methacrylate, 236 parts by weight of isobornyl methacrylate, 64 parts by weight of 4-hydroxybutyl acrylate, 250 parts by weight of t-butylstyrene, 110 parts by weight of t-butylperoxy 2-ethylhexanoate and xylene A solution consisting of 150 parts by weight was prepared and dropped from the dropping funnel into the above reaction vessel over 3 hours. The solution temperature was kept at 130 ° C.
[0116]
After maintaining at 130 ° C. for 30 minutes after the completion of the dropwise addition, a solution comprising 10 parts by weight of t-butylperoxy 2-ethylhexanoate and 50 parts by weight of xylene was added dropwise over 30 minutes. After completion of the dropwise addition, the reaction was further continued at 130 ° C. for 1 hour, and then 270 parts by weight of the solvent was removed, and an acrylic polyepoxide having a number average molecular weight of 2,200, an epoxy equivalent of 316 and a hydroxyl value of 25 mgKOH / g (solid content) was obtained. And a varnish having a nonvolatile content of 72% by weight.
[0117]
Example 1
Preparation of water-based base paint 164 parts of the water-soluble amide group-containing acrylic resin 1 obtained in the previous production example, 80 parts of the water-soluble acrylic resin 2 obtained in the previous production example, and an aluminum pigment paste " 19 parts of aluminum paste MH-8801 "(manufactured by Asahi Kasei Corporation) and uniformly dispersed. Further, 50 parts of melamine resin" Cymel 202 "(manufactured by Mitsui Cytec), and crosslinkable resin particles (manufactured by Nippon Paint Co., Ltd., dynamic light) 10 parts of an average particle size of 55 nm by a scattering method, a solid content of 20%, and a xylene solution, and 10 parts of dimethylethanolamine (boiling point: 135 ° C., half equivalent potential point: −15 mV) were added to give 21.3 parts (5.0 equivalents). ) And further uniformly dispersing, whereby an aqueous base coating material 1 was obtained. In addition, the compounding amount (part) of the acrylic resin and the melamine resin was represented by solid content.
[0118]
Next, the sample was diluted for 50 seconds (measured at 20 ° C. using a No. 4 Ford cup) using ion exchanged water as a dilution medium. The obtained diluted aqueous base paint 1 had a solid content of 24%.
[0119]
Further, the curing start time of the obtained base coating material was measured by a free damping vibration type viscoelasticity measuring device (hereinafter referred to as “FDOM”), and the time when the coating film temperature reached a predetermined baking temperature was zero (± 0). ), The decrease start time obtained from the plot of the vibration period measurement value was obtained as the reaction start time.
[0120]
Specifically, the reaction start time is measured by using a rigid pendulum type physical property tester “DDV-OPAIII” manufactured by Orientec Co., and applying a coating material on the metal support so that the dry base film thickness is 12 μm. After setting in a room at a temperature of 25 ° C. and 60% RH for 3 minutes, the temperature of the coating film is raised to 30 ° C. after 1 minute, and to 140 ° C. after 10 minutes from 30 ° C., and maintained at 140 ° C. for 20 minutes. The test was performed under the following conditions. The reaction start time was defined as ± 0.0 minutes when the temperature of the base coating film reached 140 ° C. The curing start time of the obtained base paint 1 was 11.2 minutes.
[0121]
Preparation of high solid type clear paint The acrylic polycarboxylic acid varnish synthesized as described above, the polyester polycarboxylic acid varnish and the acrylic polyepoxide varnish were each 24 parts by weight of a nonvolatile component: 25 parts by weight: 51 parts by weight. Parts, mixed with 0.5 parts by weight of a tetrabutylammonium bromide curing catalyst, 0.5 parts by weight of a dibutyltin bis (butylmalate) catalyst, 2 parts by weight of an ultraviolet absorber (“Tinuvin 900” manufactured by Ciba Geigy), and photostable. 1 part by weight of an agent ("Sanol LS-440" manufactured by Mitsui Co., Ltd.) and 0.1 part by weight of a surface conditioner ("Modaflow") were mixed with a disperser while stirring. The equivalent ratio of carboxyl group / epoxy group of the obtained paint was 100/96.
[0122]
The obtained paint was diluted with a thinner consisting of ethyl 3-ethoxypropionate / S-150 (manufactured by Esso) = 1/1 to a coating viscosity (Ford Cup No. 4, 35 seconds at 20 ° C.). A solid clear paint was prepared. 0.5 ± 0.1 g of the paint was precisely weighed, the mass of the paint after drying at 110 ± 5 ° C. for 60 minutes was precisely weighed, and the non-volatile calculated by dividing the mass of the paint before drying by 100 times. Min was 56.0% by weight and VOC was 440 g / l.
[0123]
The curing start time of the obtained clear paint was measured by "FDOM" in the same manner as in the base paint. Specifically, the reaction start time was measured using a rigid pendulum type physical property tester “DDV-OPAIII” manufactured by Orientec Co., Ltd. to apply a clear coating film to a thickness of 40 μm. The curing start time of the obtained clear paint was 12.0 minutes.
[0124]
Coating method : After subjecting two dull steel plates having a size of 30 cm × 40 cm and a thickness of 0.8 mm to a zinc phosphate treatment, a cationic electrodeposition coating material “Power Top V-6” (manufactured by Nippon Paint Co., Ltd.) and an intermediate coating material “Olga P” -Gray "(manufactured by Nippon Paint Co., Ltd.) was applied to the substrate, and the previously diluted aqueous base paint was applied using an externally-applicable" metabell "to a dry film thickness of 15 [mu] m. Two-stage coating was performed at 60 kV, a rotation speed of 25,000 rpm, a shaving air pressure of 3.5 kg / cm ² , and a discharge rate of 120 cc / min. There was a 1.5 minute interval between the two applications. After setting for 3 minutes after the second coating, preheating was performed at 80 ° C. for 3 minutes.
[0125]
Next, the high solid type clear paint of the above-mentioned production example was applied to the aqueous base coated plate obtained above using a “micro microbell” so as to have a dry film thickness of 40 μm using an applied voltage of −90 kV and a rotation speed of One stage coating was performed at 30,000 rpm, a shaving air pressure of 1.5 kg / cm ² , and a discharge rate of 280 cc / min, and the setting was performed for 7 minutes. Next, the obtained two coated plates were baked for 20 minutes in a dryer at 120 ° C. and 140 ° C., respectively.
[0126]
The coated plate obtained by baking at 140 ° C. was visually evaluated with respect to the coating film appearance, particularly the glossiness, according to the following evaluation criteria.
<Glossiness criteria>
5; very glossy 4; glossy 3; glossy 2; slightly glossy 1; no gloss
After leaving the two metallic coating films obtained by baking at 120 ° C. and 140 ° C. for 24 hours, they were immersed in high-temperature water at 80 ° C. for 3 hours. After raising, 100 grids of 2 mm were formed using a cutter knife so as to reach the substrate, and the adhesion was evaluated by a tape peeling method. Of the 100 grids, the number of grids in the grid that did not peel off was indicated as the adhesion result.
Table 1 shows the results.
[0128]
Examples 2 to 4, Comparative Examples 1 to 3
The tertiary amines shown in Table 1 were used to neutralize the carboxyl groups of the film-forming resin used in the production of the water-based metallic base paint at the indicated equivalent ratios. The curing start time was measured. Similarly, a laminated coated plate was prepared and evaluated. The results are shown in Table 1.
[0129]
[Table 1]

[0130]
From the results in Table 1, according to the coating film forming method of the present invention, a laminated coating film having excellent appearance was able to be obtained. In particular, even in a coating film baked and cured at a low temperature, an excellent coating film without delamination could be formed in a high-temperature water resistance test.
[0131]
On the other hand, in the comparative example, the system using the base paint containing a tertiary amine having a low boiling point had a reduced appearance, and the one having a low basicity was considered to have reduced the curability of the coating film. Sex decreased.
[0132]
【The invention's effect】
That is, according to the coating film forming method of the present invention, even in the two-coat one-bake coating method, the curing speed of the base coating film is governed by the basicity of the tertiary amine contained therein, and the curing speed of the adjacent carboxylic acid / epoxy hardened. The curing speed of the system clear is governed by the nucleophilicity of the tertiary amine transferred from the base coating, so that the curing balance of each coating is optimized and a laminated coating with extremely high quality coating appearance is formed. It seems to have been able to. That is, it is considered that the transfer of the tertiary amine at the time of baking improved the coating film performance by sufficiently proceeding the crosslinking of the clear without impairing the stability of the present clear.
[0133]
In other words, this technique makes it possible to efficiently and effectively approach the difference in the curing speed between the base coating film and the clear coating film, thereby reducing the deterioration in the finished appearance due to the curing distortion caused by the difference in the curing speed between the layers. It was possible to achieve an extremely high finished appearance without any adverse effect on other performances.
[0134]
In addition, the high solid type clear paint used in the examples has a low VOC and a high non-volatile content in the coating viscosity, so that the amount of volatile organic solvent can be reduced and the number of exhaust treatment steps can be reduced, and the triazine ring is not contained. It shows great resistance to acid rain and is ideal for automotive topcoats.

Claims (3)

In a two-coat, one-bake coating forming method for sequentially applying a water-based base coating and a clear coating on a substrate by wet-on-wet,
The aqueous base coating composition contains a carboxyl group-containing resin and a tertiary amine having a half-equivalent point potential of −60 to 0 mV in a potentiometric titration and a boiling point of 120 to 290 ° C. 1.5 to 7.0 equivalents of
In addition, the clear paint is a carboxylic acid / epoxy group-curable paint, and is a high solid type clear paint having a VOC of 400 to 550 in a diluted paint diluted to a coating viscosity. The carboxyl group-containing resin further contains an acrylic resin containing a carboxyl group and an amide group, and the solid content weight ratio of the carboxyl group and the amide group-containing acrylic resin to the other carboxyl group-containing resin is 30. The coating film forming method according to claim 1, wherein the ratio is from / 70 to 90/10. A laminated coating film formed by the method according to claim 1.